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dd133 · 05-17-2010, 09:58 AM

A friend gave me a Marshall TSL 100 Watt. He said it worked but there was barely any volume . I checked it out and found 3 output tubes crapped out so that explains the volume drop. I changed the power tubes with Winged C's EL34's and noticed that the bias test points were loose so i opened up the amp to find cold solder joints (common problem) so after resoldering the bias supply pcb i also checked the bias resistors which were fine. Then I just put the amp on standby and let it warm up for 10 mins.

I checked the tube bias and got a reading of 180ma on V5, V6 which is way too high but the other side V7, V8 was fine. I tried to lower the bias on V5,V6 but wasn't able to get any lower than 118ma, i was able to bias V7,V8 from 100ma to 40ma normally.

Does any one have an idea of what this problem might be?

05-17-2010, 09:58 AM	#1 (permalink)
dd133 Junior Member Join Date: Apr 2010 Posts: 7	TSL Bias Too Hot 118ma? A friend gave me a Marshall TSL 100 Watt. He said it worked but there was barely any volume . I checked it out and found 3 output tubes crapped out so that explains the volume drop. I changed the power tubes with Winged C's EL34's and noticed that the bias test points were loose so i opened up the amp to find cold solder joints (common problem) so after resoldering the bias supply pcb i also checked the bias resistors which were fine. Then I just put the amp on standby and let it warm up for 10 mins. I checked the tube bias and got a reading of 180ma on V5, V6 which is way too high but the other side V7, V8 was fine. I tried to lower the bias on V5,V6 but wasn't able to get any lower than 118ma, i was able to bias V7,V8 from 100ma to 40ma normally. Does any one have an idea of what this problem might be?